Means and method for the continuous nondestructive testing of metallic strip and the like

ABSTRACT

Apparatus and procedures for accurately determining the quality of metallic strip or other essentially homogenous materials by multiplying direct current voltages which are the functions of (a) the magnitude of defect indications and (b) strip speed, accumulating the multiplied voltages, and dividing the accumulated voltages by a proportional figure representing the total length of material tested.

United States Patent Inventor Don L. Conn Middletown, Ohio Appl. No.842,264

Filed July 16, 1969 Patented Oct. 12, 1971 Assignee Armco SteelCorporation Middletown, Ohio MEANS AND METHOD FOR THE CONTINUOUSNONDESTRUCTIVE TESTING OF METALLIC STRIP AND THE LIKE 25 Claims, 4Drawing Figs.

US. Cl 235/15l.3, 73/104, 73/159 Int. Cl G0lb 19/32, G0ln 19/08 Field ofSearch 73/679,

67.8,105, 104, 159;235l151.35,15l.l3, 151.3; 324/34 TA; 25( )/2l9 DF,83.3 D

[56] References Cited UNITED STATES PATENTS 3,278,747 10/1966 Ohmart250/833 D 3,019,346 1/1962 Laycak 250/219 DF Primary ExaminerEugene G.Botz Attorney-Melville, Strasser, Foster & Hoffman ABSTRACT: Apparatusand procedures for accurately determining the quality of metallic stripor other essentially homogenous materials by multiplying direct currentvoltages which are the functions of (a) the magnitude of defectindications and (b) strip speed, accumulating the multiplied voltages,and dividing the accumulated voltages by a proportional figurerepresenting the total length of material tested.

V (L) Q INTEGRATOR PATENTEUUCT 121971 3,512, 3

SHEET 10F 2 MATL :LENGTH v L 9 (u [0 n L MATL SPEED pa 5 (s) MULTIPLIER5 4 (8d) 8 L MAT'L F- DEFECT (d) 6 INTEGRATOR d Af '"'\F FIG. I

MAT'L DIVIDER LENGTH Q L 9 (L) L lo 8 a MATL s 9 SPEED QUULTIPLIER kl? 5S 4 Ysd) L MAT'L c 7 6 DEZECT (d) INTEGRATOR A 3 2 I FIG. 2

lNVENTOR/S DON L. CONN ATTORNEYS PATENTEDUBT l2 l9?! MATL LENGTH MATLSHEET 20F 2 SPEED MR MAT'L DEFECT DEPTH f MATL DEFECT WIDTH My) MATLLENGTH MULTIPLE-IR f gg y) INTEGRATOR MULTIPLIE R FIG. 3

MATL sPEED MATL DEFECT DEPTH DIVIDER S dxdy) MULTIPLIER IN TE GRATOR 7MULTIPL [ER lNVENTOR/S DON L. CONN BY DEE M, 2;

ATTORNEYS FIG. 4

MEANS AND METHOD FOR THE CONTINUOUS NONDESTRUCTIVE TESTING OF METALLICSTRIP AND THE LIKE BACKGROUND OF THE INVENTION The present inventionrelates to the nondestructive testing of essentially homogenousmaterials to determine the presence and extent of defects in thematerial being tested, thereby enabling the producer to establishquality control standards and accurately grade the quality of a givenrun of material. While its utility is not so limited, the presentinvention will be described in connection with the inspection of steelstrip as it is produced in a steel mill, such strip usually being rolledinto continuous lengthsof from two to three thousand feet. As willbecome evident, however, the apparatus and procedures herein describedmay be readily applied to the testing of diverse materials, as well asto materials other than a strip form, as for example, materials in theform of blocks, billets, or tubing. I

Nondestructive testing procedures as such are well known and defects ina metallic strip, such as mechanical pipe or voids, inclusions, andsegregations or differences in density have hitherto been detected byultrasonic inspection wherein a beam of ultrasonic energy is directedinto the material being tested and either its transmitted or reflectedenergy measured, inspection being accomplished because the ultrasonicbeam will travel with little energy loss through essentially homogenousmaterials except when intercepted and reflected by discontinuities inthe elastic continuum. Such defects also have been detected byelectromagnetic induction, the material being tested being placed in themagnetic field of a coil or an array of conductors carrying analternating current which induces eddy currents in the material, themagnitude of which will vary depending upon the presence of defects. Athird known procedure for nondestructive testing involves thermal orinfrared testing based on measuring the rate of flow of heat through thematerial, the rate varying depending upon the presence and extent of theinternal defects encountered.

Experience has indicated that the performance of a given strip ofmaterial in the hands of the user can be predicted in accordance withthe extent of the defects which are encountered; and a grading systemhas been developed in which a quality number is assigned to the materialbased on the inspection results. The quality number may be defined as anumber indicative of the total defect areas of the strip divided by itstotal length. A defect area in the moving strip is usually measured bymeans of two parameters, defect depth, which is the depth of the defectcompared to the thickness of the material, as determined by theamplitude of the signal received by the defect-detecting device, anddefect length, as determined by the length of time the defect isdisplayed by the defect-detecting device. The defect area (or magnitudeof defeet) is thus the product of defect depth and defect length, andthe sum total of the individual defect areas (magnitude of defects)divided by total strip length gives the quality number. While thisapproach has resulted in a workable system which has been used with somesuccess, numerous difficulties are encountered in interpreting andevaluating the test results.

In a typical example of currently employed nondestructive testingprocedures, the test results (the number and magnitude of defectindications) are recorded on a strip chart recorder and are thereaftervisually evaluated, the operator manually calculating what he believesto be the total defective area. The length of the strip is alsophysically measured to determine its length, and the quality numbercalculated by dividing the manually computed defective material area bythe total material length. Such procedure is subject to numerous errorsand inaccuracies, and is also subject to considerable variationsdepending upon the interpretation of the strip chart recording by theoperator. For example, variations in the speed of travel of thematerial, or stoppage of the material, can cause large errors in therecorded results in that the recorded defect length will vary with stripspeed. If the strip speed is slowed by one-half, the recorded defectlength will be doubled as compared to the recorded defect length of thesame defect measured at original speed. Where defect indications arenumerous, counting errors are almost assured, particularly when it isconsidered that a strip chart in a few feet of length will record defectindications for several thousand feet of strip. It is literallyimpossible to run the material at a constant speed due to speed-up asthe strip is started in motion, and slowdown as it is stopped; andit isusually at the ends of the strip that defects are most commonlyencountered. Operator judgment varies widely, as do individualevaluating techniques; consequently there may be as much as 5 -l0percent variation between different operators interpretation of a givenstrip chart. Such variations obviously result in marked differences inquality standards depending upon operator judgment and ability.

While it has hitherto been proposed to drive the strip chart recorder insynchronism with the speed of travel of the material, such efforts havebeen only partially successful and significant variations in resultsstill occur. This is particularly true in endeavoring to accuratelycalculate the area of a given defect. An accurate quality number shouldbe a function of magnitude of the defects detected as well as the merenumber of defects.

RESUME OF THE INVENTION A principal object of the present invention isthe elimination of operator judgment in the nondestructive testing ofcontinuously moving materials by providing a procedure and apparatuswhich accurately measures and computes both the number and area ofdefect indications independently of material speed variations and eitherautomatically calculates a quality number directly or provides tworeadings from which the quality number can be readily calculated by theoperator.

In accordance with the invention, two direct current voltages aregenerated, the first being a function of the magnitude of a defectindication, d, and the second a function of strip speed, S. These. twovoltages are multiplied to produce an output voltage which is theproduct of strip speed and defect magnitude Sd per unit of time. Theoutput voltage is accumulated and the total charge stored. At the end ofthe inspection run the accumulated voltage may be represented as:

(1)295 l+ 1+ which accurately represents the total defective area of thestrip. At the same time, the total length or footage of the strip beinginspected is measured and, in a preferred embodiment of the invention, avoltage generated which is proportional to the length of the strip. Thequality number is then obtained by dividing the total defective area bythe total length:

In accordance with the invention the division can be performed eithermanually or automatically. If manual, voltmeters or electronic counterswill be provided to give visual readings of the accumulated voltagesrepresenting both total defective strip area and total strip length.Alternatively, the accumulated voltages can be fed to an electronicdivider which will automatically perform the division, the readout of=Quality Number the divider representing the quality number of thematerial being tested.

While for practical purposes the quality number of equation II providesan accurate indication of strip performance, it is also within thespirit and purpose of the invention to additionally measure defectwidth, which may be defined as the lateral or crosswise extent of adefect, thereby giving a reading which is indicative of defect volume.Thus, three direct current voltages are generated, the first being afunction of the magnitude of a defect indication showing the depth ofthe defect 11,, and the second a function of the magnitude of a defectindication showing the width of the defect d,,relative to the totalwidth of the material being tested. These two voltages are multiplied toproduce a first output voltage which is the product of defect depth anddefect width d a ,,and such output voltage is then multiplied by a thirdvoltage which is the function of strip speed S, thereby producing asecond output voltage which is the product of defect depth X defectwidth x defect length. The second output voltage is accumulated and thetotal charge stored, so that at the end of the inspection run theaccumulated voltage may be represented as:

zllf l rl ul 2 z2 uz+ n rn un which accurately represent the totaldefective volume of the strip. At the same time, the total length of thestrip is measured, and a voltage generated which is proportional to thetotal volume of the strip (V total strip length strip thickness X stripwidth). The quality number is then obtained by dividing the totaldefective volume by the total volume:

As before, the division can be performed either manually orautomatically. If desired, the quality number can be computed based ontotal strip length L rather than on volume V since for some applicationsan indication of defect volume relative to strip length will providesufficiently accurate information for control purposes.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of areadout system in accordance with the invention in which the qualitynumber is manually calculated.

FIG. 2 is a similar schematic representation of a readout system inwhich the quality number is automatically computed.

FIG. 3 is a schematic representation of a readout system for determiningdefect volume, the quality number being manually calculated.

FIG. 4 is a schematic representation of a system for determining defectvolume wherein the quantity number is automatically computed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawing,the strip material being inspected is indicated at l, the strip movingin the direction of the arrow A. In accordance with the invention, adefect signal is obtained using any of the known nondestructive testingdevices 2 which will generate a voltage d proportional to the magnitudeof the defect. This device may comprise an ultrasonic unit having awheel 3 coupling it to the material being tested, or it may comprise aunit which induces eddy currents in the material being tested, or it maybe a thermal testing unit which gauges the rate of flow of heat in thematerial. Such devices are all well known and each is capable ofgenerating a readout voltage proportional to the defects encountered.

Material speed S is determined by a material speed transducer 4, whichpreferably comprises a tachometer generator driven by a wheel 5 whichalso contacts the strip, the tachometer generator producing an outputvoltage directly proportional to strip speed. Alternatively, an opticalpickup pulse generator may be employed, the primary requisite of thespeed transducer being the production of an output voltage which is afunction of material speed.

The output voltages d and S are fed to a multiplier 6 which comprises adevice capable of producing an output voltage proportional to theproduct of the input signals d and S. The multiplier 6 may comprise aHall-Effect multiplier, or it may be an electronic multiplier, such as amultiplier module which utilizes one of the input signals to vary thetransconductance of an input transistor stage which in turn amplifiesthe other input signal. A servomultiplier also may be employed in whichmultiplier potentiometers perform functional multiplication.

The output of the multiplier 6, which has been previously representedas:

is fed to integrator 7 which accepts the output of the multiplier andstores the accumulated charge. The integrator may comprise a singleinput analog integrator which is utilized as a straight-forward voltageamplifier, or a digital integrator may be employed in whichrepresentative samplings of a varying function results in a series ofanalog voltages, which when converted to digital numbers through the useof an analog to digital converter, can be added to obtain a numberrepresenting the total area under the function, i.e., integration bysummation. In the embodiment of FIGURE 1, the output of the integrator 7is read on a digital voltmeter 8 which possesses the high inputresistance and precision required to accurately measure the outputvoltage of the integrator without appreciable loading error.

It is also necessary in the systems of both FIGURES I and2 toconcurrently measure the total length or footage L of the material beingtested. This may be conveniently done by means of a footage indicator 9which also may have a wheel 10 contacting the strip 1, although as apractical matter the footage indicator may be operatively connected toand driven by the wheel 5 of the material speed transducer 4. Thefootage indicator preferably will be of the type which will produce avoltage proportional to strip length which can be read directly from avoltmeter II where the system of FIGURE I is employed. Alternatively, amechanical counter can be employed to provide a direct numerical readingof strip length.

As should now be evident, the system of FIGURE 1 provides the operatorwith a readout at voltmeter 8 which accurately represents the totalmeasured defective area irrespective of strip speed, and the readout atvoltmeter (or counter) 10 represents the total measured length of striptested. The operator may then readily compute the quality numberapplicable to the material being tested by dividing the total defectivearea by the total length:

E n M%%l Quality Number It will be understood that the quality numberis, in effect, a measure of the percentage of the total length of thematerial which is defective, and as long as the readout of the meters 8and 11 are in directly proportional units of comparable value, vizproportional voltages, the quality number will be a direct percentagereading. The values of the readout units may be arbitrarily chosen, withthe quality number representing a figure on an arbitrarily chosen scale,as where a voltage readout is divided by strip length in feet. Ifdesired, a sealer may be employed to divide large magnitude numbers forsimplified computation.

Instead of manually calculating the quotient in formula (II) above, thesystem may, as illustrated in FIGURE 2, incorporate a divider 12 whichembodies an electronic division circuit which will automatically computethe quality number by dividing the output voltage of the integrator 7 bythe output of a voltage producing footage indicator 9, the dividedvoltage being read on a calibrated voltmeter 13. In this connection itmay be noted that certain types of multipliers, such as electronicmultipliers, will also divide when properly connected, and consequentlyit is to be understood that the division operation, in some instances,may be performed by operating components of the multiplier.

In the embodiment of FIGURE 3 provision is made for the addition of athird parameter in determining the magnitude of the defects encountered,such additional parameter contemplating defect width d,,which, whenmultiplied by defect depth d and defect length S, provides an accurateindication of defect volume V. Generally speaking, the addition of suchthird parameter is only of importance in the testing of materials suchas billets or slabs which have significant dimensions in both directionsperpendicular to their path of travel during testing. For purposes ofsimplicity like parts have been given like reference numerals, and itwill be seen that the system of FIGURE 3 incorporates the mechanisms ofFIGURE 1 with the addition of a second nondestructive testing device 211oriented to generate a voltage proportional to the width of the defectencountered. This proportional voltage, together with the proportionalvoltage generated by testing device 2 which measures defect depth, isfed into multiplier 6 which produces a first output voltage which is theproduct of defect depth and defect width. This output voltage is fed toa second multiplier 60 which also receives the proportional voltagegenerated by material speed transducer 4, the multiplier 6a generatingan output voltage proportional to the product of the input signals,which in this instance represents defect volume in accordance withequation (lll) above. The output voltage of multiplier 6a is fed tointegrator 7 which shows the accumulated charge, the accumulated chargebeing indicated on voltmeter 8. As in the case of the embodiment ofFIGURE 1, the total length of the material being tested is measured byfootage indicator 9 which produces a proportional voltage readable onvoltmeter l1.

The operator may readily compute the quality number in accordance withequation (lV) above, the quality number being either a measure of stripdefect to total length or to total volume, as desired.

In the embodiment of FIGURE 4 wherein like components have again beengiven like reference numerals, provision is made for automaticallycomputing the quality number, the outputs of integrator 7 and footageindicator 9 being fed to the divider 12 which will automatically computethe quality number. ln this connection the divider 12 can be programmedto compute total strip volume by multiplying total strip length by knownstrip thickness and width, which are normally constant, therebyproducing a quality number at voltmeter 13 which is a direct percentagereading of total defect volume to total strip volume.

As should now be apparent, the instant invention provides a highlyaccurate testing procedure and apparatus which is free from operatorjudgment and variations in measuring techniques and provides a qualitynumber which is independent of material speed variations and hence atruly accurate indicator of strip quality. It is to be understood thatmodifications may be made in the invention without departing from itsspirit and purposes. Various such modifications have already beenindicated, and others will undoubtedly occur to the skilled worker inthe art upon reading this specification. For example, where stripthickness and/or strip width might be variable, additional measuringdevices may be included to generator proportional voltages indicative ofsuch variations, which may be utilized to compute total strip volume.Should a situation arise where the signals generated by a plurality ofthe testing devices interfere with each other, the units may bedisplaced relative to each other with the provision of means to delaythe signal from the leading sensing unit.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In combination in apparatus for the continuous nondestructive testingof essentially homogenous materials,

means for generating a first voltage which is a function of themagnitude of material defects,

means for generating a second voltage which is a function of materialspeed,

means for multiplying said first and second voltages to produce anoutput voltage which is the product of said first and second voltages,

means for accumulating the said output voltage,

means for measuring the total length of the material being tested, and

readout means for indicating values for at least total strip length andaccumulated output voltage.

2. The apparatus claimed in claim 1 wherein said means for measuring thetotal length of the material comprises means producing a voltageproportional to material length.

3. The apparatus claimed in claim 2 wherein said readout means comprisesa first voltmeter for indicating the voltage output of said strip lengthmeasuring means, and a second voltmeter for indicating the accumulatedoutput voltage of said accumulating means.

4. The apparatus claimed in claim 2 wherein said readout means includesdivider means for dividing the output voltage accumulated by saidaccumulating means by the output voltage of said strip length measuringmeans.

5. The apparatus claimed in claim 1 wherein said accumu lating meanscomprises an analog integrator.

6. The apparatus claimed in claim 1 wherein said accumulating meanscomprises a digital integrator.

7. The apparatus claimed in claim 1 wherein said multiplying meanscomprises a Hall-Effect multiplier.

8. The apparatus claimed in claim 1 wherein said multiplying meanscomprises an electronic multiplier.

9. The apparatus claimed in claim 1 wherein said means for generatingsaid first voltage comprises an eddy current testing means.

10. The apparatus claimed in claim 1 wherein said means for generatingsaid first voltage comprises a thermal testing means.

11. The apparatus claimed in claim 1 wherein said multiplying meanscomprises a servomultiplier.

12. The apparatus claimed in claim 1 wherein said means for generatingsaid first voltage comprises an ultrasonic testing means.

13. The apparatus claimed in claim I wherein the means for generatingsaid second voltage comprises a material speed transducer such as atachometer generator.

14. The apparatus claimed in claim 1 wherein the means for generating afirst voltage which is a function of the magnitude of material defectsincludes means for generating voltages proportional to both defect depthand defect width, and means for multiplying said proportional voltagesto generate said first voltage.

15. The apparatus claimed in claim 14 wherein the means for measuringtotal material length comprises means producing a voltage proportionalto total material length, and includes means for producing voltagesproportional to material width and material thickness, and wherein saidreadout means includes means for multiplying the proportional voltagesrepresenting total material length, material width and materialthickness to produce an output voltage representing total materialvolume, and means for dividing the output voltage accumulated by saidaccumulating means by the output voltage representing total materialvolume.

16. A procedure for the continuous nondestructive testing of essentiallyhomogenous materials which comprises the steps of:

advancing said material in a path of travel,

generating a first voltage which is a function of the magnitude ofdefects detected in the strip,

generating a second voltage which is a function of material speed,

multiplying said first and second voltages to produce an output voltagewhich is the product of said first and second voltages, accumulatingsaid output voltage and establishing a numerical value for saidaccumulated output voltage, and

measuring the total length of the material being tested and establishinga numerical value for the total length of the said material.

17. The procedure claimed in claim 16 including the step of establishinga quality number for said material by dividing the numerical value ofsaid accumulated voltage by the numerical value of the total length ofsaid material.

18. The procedure claimed in claim 16 wherein the total length of thematerial is measured by generating a voltage which is proportional tomaterial length.

19. The procedure claimed in claim 16 including the step of establishinga quality number for said material by dividing the said accumulatedoutput voltage by the voltage which is proportional to total materiallength.

20. The procedure claimed in claim 16 including the step ofultrasonically vibrating the material being tested, and generating saidfirst voltage in response to the ultrasonic vibration of the materialbeing tested.

21. The procedure claimed in claim 16 including the step of inducingeddy currents in the material being tested, and generating said firstvoltage in response to eddy currents induced in the material beingtested.

22. The procedure claimed in claim 16 including the step of causing heatto flow through the material being tested, and generating said firstvoltage in response to the rate of flow of heat through the materialbeing tested.

23. The procedure claimed in claim 16 including the step of generatingvoltages proportional to both defect depth and defect width andmultiplying said proportional voltages to produce said first voltage.

24. The procedure claimed in claim 23 including the step of establishinga numerical value for the total volume of the material, and establishinga quality number for said material by dividing the numerical value ofsaid accumulated voltage by the numerical value of the total volume ofthe material.

25. The procedure claimed in claim 23 wherein the total length of thematerial is measured by generating a voltage which is proportional tomaterial length, and including the steps of generating voltagesproportional to material width and material thickness, multiplying thevoltages so generated to produce an output voltage which is proportionalto total material volume, and establishing a quality number for saidmaterial by dividing the said accumulated output voltage by the outputvoltage which is proportional to material volume.

1. In combination in apparatus for the continuous nondestructive testingof essentially homogenous materials, means for generating a firstvoltage which is a function of the magnitude of material defects, meansfor generating a second voltage which is a function of material speed,means for multiplying said first and second voltages to produce anoutput voltage which is the product of said first and second voltages,means for accumulating the said output voltage, means for measuring thetotal length of the material being tested, and readout means forindicating values for at least total strip length and accumulated outputvoltage.
 2. The apparatus claimed in claim 1 wherein said means formeasuring the total length of the material comprises means producing avoltage proportional to material length.
 3. The apparatus claimed inclaim 2 wherein said readout means comprises a first voltmeter forindicating the voltage output of said strip length measuring means, anda second voltmeter for indicating the accumulated output voltage of saidaccumulating means.
 4. The apparatus claimed in claim 2 wherein saidreadout means includes divider means for dividing the output voltageaccumulated by said accumulating means by the output voltage of saidstrip length measuring means.
 5. The apparatus claimed in claim 1wherein said accumulating means comprises an analog integrator.
 6. Theapparatus claimed in claim 1 wherein said accumulating means comprises adigital integrator.
 7. The apparatus claimed in claim 1 wherein saidmultiplying means comprises a Hall-Effect multiplier.
 8. The apparatusclaimed in claim 1 wherein said multiplying means comprises anelectronic multiplier.
 9. The apparatus claimed in claim 1 wherein saidmeans for generating said first voltage comprises an eddy currenttesting means.
 10. The apparatus claimed in claim 1 wherein said meansfor generating said first voltage comprises a thermal testing means. 11.The apparatus claimed in claim 1 wherein said multiplying meanscomprises a servomultiplier.
 12. The apparatus claimed in claim 1wherein said means for generating said first voltage comprises anultrasonic testing means.
 13. The apparatus claimed in claim 1 whereinthe means for generating said second voltage comprises a material speedtransducer such as a tachometer generator.
 14. The apparatus claimed inclaim 1 wherein the means for generating a first voltage which is afunction of the magnitude of material defects includes means forgenerating voltages proportional to both defect depth and defect width,and means for multiplying said proportional voltages to generate saidfirst voltage.
 15. The apparatus claimed in claim 14 wherein the meansfor measuring total material length comprises means producing a voltageproportional to total material length, and includes means for producingvoltages proportional to material width and material thickness, andwherein said readout means includes means for multiplying theproportional voltages representing total material length, material widthand material thickness to produce an output voltage representing totalmaterial volume, and means for dividing the output voltage accumulatedby said accumulating means by the output voltage representing totalmaterial volume.
 16. A procedure for the continuous nondestructivetesting of essentially homogenous materials which comprises the stepsof: advancing said material in a path of travel, generating a firstvoltage which is a function of the magnitude of defects detected in thestrip, generating a second voltage which is a function of mateRialspeed, multiplying said first and second voltages to produce an outputvoltage which is the product of said first and second voltages,accumulating said output voltage and establishing a numerical value forsaid accumulated output voltage, and measuring the total length of thematerial being tested and establishing a numerical value for the totallength of the said material.
 17. The procedure claimed in claim 16including the step of establishing a quality number for said material bydividing the numerical value of said accumulated voltage by thenumerical value of the total length of said material.
 18. The procedureclaimed in claim 16 wherein the total length of the material is measuredby generating a voltage which is proportional to material length. 19.The procedure claimed in claim 16 including the step of establishing aquality number for said material by dividing the said accumulated outputvoltage by the voltage which is proportional to total material length.20. The procedure claimed in claim 16 including the step ofultrasonically vibrating the material being tested, and generating saidfirst voltage in response to the ultrasonic vibration of the materialbeing tested.
 21. The procedure claimed in claim 16 including the stepof inducing eddy currents in the material being tested, and generatingsaid first voltage in response to eddy currents induced in the materialbeing tested.
 22. The procedure claimed in claim 16 including the stepof causing heat to flow through the material being tested, andgenerating said first voltage in response to the rate of flow of heatthrough the material being tested.
 23. The procedure claimed in claim 16including the step of generating voltages proportional to both defectdepth and defect width and multiplying said proportional voltages toproduce said first voltage.
 24. The procedure claimed in claim 23including the step of establishing a numerical value for the totalvolume of the material, and establishing a quality number for saidmaterial by dividing the numerical value of said accumulated voltage bythe numerical value of the total volume of the material.
 25. Theprocedure claimed in claim 23 wherein the total length of the materialis measured by generating a voltage which is proportional to materiallength, and including the steps of generating voltages proportional tomaterial width and material thickness, multiplying the voltages sogenerated to produce an output voltage which is proportional to totalmaterial volume, and establishing a quality number for said material bydividing the said accumulated output voltage by the output voltage whichis proportional to material volume.